1. Field of the Invention
The present invention relates to an optical apparatus having a shake correction function and a control method thereof, and an image pickup apparatus.
2. Description of the Related Art
Optical hand shake correction is used to correct a shake applied to an optical apparatus, e.g., an image pickup apparatus such as a still camera and a video camera. In the optical hand shake correction, a shake is detected from an image formed on an image pickup device, a target position of a shift lens is determined based on a detected amount of shake, and the shift lens is moved to the target position in a direction perpendicular to an optical axis. At that time, e.g., feedback control is performed to reduce a deviation between the target position and an actual position to zero.
A mechanism for such shake correction should preferably have characteristics that a friction occurring therein is small, a target tracking ability thereof is excellent, and resonance frequencies thereof can easily be designed. A shake correction mechanism having such characteristics has been proposed (see, for example, Japanese Laid-open Patent Publication No. 2001-290184), in which a plurality of balls are held between a stationary barrel and a movable barrel that retains a shift lens, and the movable barrel is urged by a spring toward the stationary barrel.
With the shake correction mechanism disclosed in Japanese Laid-open Patent Publication No. 2001-290184, if each ball is located between limit ends of a ball receiving portion of the stationary barrel, a rolling friction state can be realized where the balls roll with movement of the movable barrel. On the other hand, if some ball remains pressed against the limit end, the rolling friction state changes to a sliding friction state in which the target tracking ability is lowered. To obviate this, the proposed shake correction mechanism performs a reset operation to drive the movable barrel to a movable limit and then returns the movable barrel to its center position, so that each ball is positioned to a central position between the limit ends.
Japanese Laid-open Patent Publication No. 7-270846 discloses a camera having a shake correction mechanism configured to be initialized by placing a shift lens at a predetermined position when a battery is mounted to the camera.
In recent years, the optical apparatus, e.g., the image pickup apparatus, is made more compact and thinner, and therefore when a lens barrel is retracted, distances between component parts of the apparatus become small. As a result, a shift lens unit sometimes interferes with a counterpart component and becomes unmovable. If a drive force for the shift lens unit varies due to interference between component parts of the image pickup apparatus, an error is caused when detecting an attitude of the apparatus based on a signal representing the drive force for the shift lens unit.